Digital lighting technologies, i.e. illumination based on semiconductor light sources, such as light-emitting diodes (LEDs), offer a viable alternative to traditional fluorescent, HID, and incandescent lamps. Functional advantages and benefits of LEDs include high energy conversion and optical efficiency, durability, lower operating costs, and many others. Recent advances in LED technology have provided efficient and robust full-spectrum lighting sources that enable a variety of lighting effects in many applications. Some of the fixtures embodying these sources feature a lighting module, including one or more LEDs capable of producing different colors, e.g. red, green, and blue, as well as a processor for independently controlling the output of the LEDs in order to generate a variety of colors and color-changing lighting effects, for example, as discussed in detail in U.S. Pat. Nos. 6,016,038 and 6,211,626, incorporated herein by reference.
It is often desirable to illuminate a wall or other surface in a manner that appears visually uniform to an observer. A uniform light distribution is generally a pleasing and non-distracting type of surface lighting. However, gaps between multiple light sources result in a non-uniform illumination pattern with adjoining brighter and darker regions. A related problem is non-uniform illumination in the vertical direction resulting in further non-uniform illumination. As a result, part of the surface typically has a bright “hot spot” that runs along the horizontal length of the surface being illuminated. One solution is to use a wider illumination beam angle, but any improvement is typically not sufficient to result in uniform luminance.
It has previously been discovered that uniform illumination is achieved on a flat surface when the light's intensity distribution is proportional to cos−3(•), where • is the angle of the light measured relative to the surface normal. However, because most installations of lighting units involve more than one light source, it is difficult to align all of the light sources to meet the mathematical requirement for uniform illumination. For example, even if a lighting unit is properly installed, the fixtures/light sources will likely not ideally align, and manufacturing tolerances create a further practical limitation on ideal alignment. Accordingly, perfect alignment and uniformity is not a feasible solution for uniform luminance of a surface.
Thus, there is a need in the art to provide an illumination pattern to achieve a visually pleasing luminance over an extended object surface, such as a wall, when using multiple light sources or multiple fixtures that are not ideally or perfectly aligned.